1. Field of the Invention
The present invention relates to a cargo handling vehicle having a push-pull unit, and more particularly to a cargo handling vehicle having a push-pull unit which comprises: a face member so mounted on the vehicle as to be movable back and forth along the forks of the vehicle; and a sheet-pallet gripper so mounted on the face member of the vehicle as to be movable in a vertical direction, so that a cargo is loaded onto the forks of the vehicle or discharged from the forks by means of the push-pull unit of the vehicle.
2. Description of the Prior Art
Heretofore, it has been known to provide a cargo handling vehicle such as a high-lift fork truck having a push-pull unit provided with the following construction.
In such conventional cargo handling vehicles: a mast is mounted on a front portion of the vehicle; forks are mounted on the mast as to be movable in a longitudinal direction or vertical direction of the mast; and a face member provided with a sheet-pallet gripper is mounted on the forks as to be movable back and forth therealong.
In the cargo loading operation of the vehicle: the face member of the push-pull unit of the vehicle is moved forward to its forward position along the forks, in which forward position the gripper of the push-pull unit grips a sheet pallet carrying a cargo; after that, the vehicle is moved forward as the face member of the push-pull unit of the vehicle is moved rearward to its rearward position along the forks, to enable the sheet pallet carrying the cargo to be loaded onto the forks, whereby the cargo loading operation of the vehicle is accomplished.
On the other hand, in the cargo discharging operation of the vehicle: under conditions where the sheet pallet carrying the cargo is released mom the gripper of the push-pull unit in the rearward position of the face member on the forks or the vehicle, the vehicle is moved rearward as the face member is moved forward to its forward position along the forks, so that the sheet pallet carrying the cargo is discharged forward from the forks of vehicle to accomplish the cargo discharging operation of the vehicle.
In the conventional cargo handling vehicle having the above construction, a hydraulic cylinder is employed to angularly control a link mechanism through which the forks are moved back and forth. On the other hand, the sheet-pallet gripper for gripping a rear end portion of the sheet pallet is provided in the face member of the vehicle, while constructed of: a sheet-pallet receiving piece fixedly mounted on a lower surface of the face member; and a presser foot vertically driven by a hydraulic cylinder as to be moved toward and away from the sheet-pallet receiving piece.
In the conventional vehicle in which the face member of the push-pull unit is moved back and forth along the forks by the hydraulic cylinder as described above, since pressurized oil is supplied to the hydraulic cylinder to actuate it when a push-pull operation lever of the vehicle is operated by an operator of the vehicle, operation of the vehicle is poor in responsibility and also poor in precise control required to effect a fine control or the face member of the push-pull unit of the vehicle so that the face member is often moved unexpectedly or jerkily.
On the other hand, in case that the presser foot of the sheet-pallet gripper is vertically driven by the hydraulic cylinder, the pressurized oil is supplied to the hydraulic cylinder through long pressurized-oil pipes provided in the vehicle, which pipes and the hydraulic cylinder lie close to the load being handled. As a result, in this case, there is a fear that a pressurized-oil leakage occurs in the hydraulic cylinder and the pressurized-oil pipe will smudge the cargo with the oil.
In the cargo loading operation of the conventional cargo handling vehicle having the push-pull unit: the presser foot of the sheet-pallet gripper of the push-pull unit is moved upward so as to be separated from the sheet-pallet receiving piece of the sheet-pallet gripper, whereby the sheet-pallet gripper is opened; then, the vehicle is moved forward so that a rear end portion of the sheet pallet carrying the cargo is inserted into a space between the presser foot and the sheet-pallet receiving piece or the sheet-pallet gripper; and after that, the presser foot of the sheet-pallet is moved downward to firmly sandwich the rear end portion or the sheet pallet between the presser foot and the sheet-pallet receiving piece or the sheet-pallet gripper. However, since the sheet-pallet gripper is provided in a lower portion of the face member of the push-pull unit of the vehicle, it is very difficult for the operator of the vehicle to watch operation of the sheet-pallet gripper while the cargo loading operation of the vehicle is performed, and, therefore it is very difficult for the operator to confirm whether or not the sheet pallet is firmly gripped by the sheet-pallet gripper.
In addition, in the cargo loading operation of the vehicle: after the rear end portion of the sheet pallet carrying the cargo is firmly gripped by the sheet-pallet gripper of the race member of the push-pull unit, the face member is moved rearward along the forks of the vehicle as the vehicle is moved forward, so that the sheet pallet carrying the cargo is loaded onto the forks of the vehicle whereby the cargo loading operation of the vehicle is accomplished.
In contrast with this, in the cargo discharging operation of the vehicle: the sheet-pallet gripper is opened to release the sheet pallet carrying the cargo from the sheet-pallet gripper of the face member; then, the face member is moved forward along the forks of the vehicle while the vehicle is moved rearward, so that the sheet pallet carrying the cargo is discharged from the vehicle to accomplish the cargo discharging operation of the vehicle. Consequently, in conventional cargo handling operation of the vehicle, first of all, the operator of the vehicle judges whether or not the cargo is loaded onto or discharged from the vehicle. Then, according to the thus judged cargo handling operation, he manually operates the sheet-pallet gripper to grip or release the sheet pallet, and after that he manually operates the face member of the push-pull unit to move the face member forward or rearward while he manually operates the vehicle to move the vehicle rearward or forward. As described above, in the conventional cargo handling operation of the vehicle, the operator of the vehicle must manually control the sheet-pallet gripper in its gripping/releasing operation, the face member in its back/forth movement, and the vehicle in its traveling operation, so that his manual operation required in cargo handling operation of the vehicle is very hard and cumbersome. In addition, in the conventional cargo handling operation of the vehicle, there is a fear that the operator mistakes operations or the sheet-pallet gripper and the face member. For example, in the cargo loading operation of the vehicle, the operator often permits the sheet-pallet gripper to release the sheet pallet therefrom by mistake, and often operates the face member to move forward by mistake. In addition, in the cargo discharging operation of the vehicle, the operator often permits the sheet-pallet gripper to grip the sheet pallet by mistake, and often operates the face member to move rearward by mistake.
It is possible to improve the cargo loading and discharging operation of the vehicle in effectiveness by keeping a traveling distance of the face member equal to that of the vehicle. However, in the conventional cargo handling operation or the vehicle, the operator must carefully operate a face-member control lever or the vehicle while he operates an accelerator pedal or the vehicle to control a traveling speed of the vehicle, so that he keeps a traveling distance of the face member equal to that of the vehicle. Consequently, it is very hard and cumbersome for the operator or the vehicle to keep a traveling distance of the face member equal to that of the vehicle during the cargo loading and discharging operation of the vehicle.